1. Field of the Invention
The present invention generally relates to a lens, and more particularly, to a fixed-focus lens.
2. Description of Related Art
The fixed-focus lens is a common optical component of an optical system, which may be used in a wide variety of applications including applications in video surveillance cameras, car cameras, back projection televisions, lenses in mobile phones, or the like. Following the development of optoelectronic technology, high quality video surveillance cameras are being more and more widely used. A high quality video surveillance camera not only may survey the ambient environment during daytime or when light is sufficient, but also has an infrared night-vision function to survey the ambient environment when light is insufficient.
In addition to having a wide angle of view to survey a large environment area, the high quality video surveillance camera is also desired to have a short and small profile to avoid affecting the appearance of the environment to thereby increase customer's willingness to buy. However, a typical five-lens fixed-focus lens used in a video surveillance camera usually has an f-number too large to use at dark night. This type of fixed-focus lens usually has an aperture stop disposed between a second lens and a third lens counted from the object side. In addition, the fixed-focus lens consisting of the five lenses usually uses at least one aspheric lens for aberration correction. However, aspheric lenses are usually difficult to fabricate and have a high cost, which makes it difficult to reduce the cost of fixed-focus lens.